Throughout this application, various publications are referenced by author and date. Full citations for these publications may be found listed alphabetically at the end of the specification immediately preceding the claims. The disclosures of these publications in their entireties are hereby incorporated by reference into this application in order to more fully describe the state of the art.
A key early event in atherogenesis is the subendothelial retention of atherogenic lipoproteins, including LDL.sup.1 (Schwenke et al., 1989; Nievelstein et al., 1991), lipoprotein(a) [Lp(a)] (Kreuzer et al., 1994), and triglyceride-rich lipoproteins (Rapp et al., 1994). Atherosclerosis-susceptible regions of the arterial tree are distinguished by their increased retention of lipoproteins compared with resistant regions (Schwenke et al., 1989). The retained lipoproteins are likely to trigger a set of biological responses, such as lipoprotein oxidation and endothelial changes (Steinberg et al., 1989; Ross, 1995), that are central to the atherogenic process (Williams et al., 1995).
Lipoproteins retained in the subendothelium are often extensively aggregated (Nievelstein et al., 1991; Hoff et al., 1985; Guyton et al., 1996). For example, Hoff and colleagues and others (see Hoff et al., 1985; Guyton et al., 1996) have shown that LDL extracted from atherosclerotic lesions is aggregated or has an increased tendency to aggregate, whereas plasma LDL exposed to the same extraction procedure as a control does not aggregate. Furthermore, Frank and colleagues (Nievelstein et al., 1991) used freeze-etch electron microscopy to demonstrate aggregated LDL in the subendothelium of the rabbit aorta as early as two hours after a large bolus injection of human LDL. Subendothelial lipoprotein aggregation is likely to be important in atherogenesis for at least two reasons. First, processes that promote lipoprotein aggregation before or during retention would be expected to increase the amount of material retained (Tabas et al., 1993). Second, aggregated LDL, but not unaggregated LDL, is a potent inducer of macrophage foam cell formation (Hoff et al., 1990; Khoo et al., 1988; Suits et al., 1989; Xu et al., 1991).